Die casting



Feb. 14, 1961 T. E. COLEMAN ETAL DIE CASTING 2 Sheets-Sheet 1 Filed Jan. 2, 1959 INVENTORS Thomas EC olem'a'n dRagmondJ.SchuPc% ATTORNEYS Feb. 14, 1961 Filed Jan. 2, 1959 T. COLEMAN ETAL 2,971,230

DIE CASTING 2 Sheets-Sheet 2 22 INVENTORS ThomasECoLeman naRagmondJschuPcg,

ATTORNEYS Unite DIE CASTING Filed Jan. 2, 1959, Ser. No. 784,804

8 Claims. (Cl. 22-68) This invention relates to die casting machines, and more particularly to devices for removing air and other gases from the die cavity of a die casting machine during the metal shooting operation.

It is known that metal die castings produced in an evacuated die cavity are more accurate, less porous, and have better surface finishes than .those manufactured in the conventional vented cavity. This improvement is due in part to the fact that the vacuum pull on the cavity permits a freer flow of metal and thus ensures complete filling of the cavity and also because it removes air and other gases which would otherwise be entrapped in the casting or produce blemishes on its surface. It is also known that the advantages of the vacuum assisted process cannot be fully availed of unless the pressure in the cavity is reduced to at least 10 inches Hg absolute and the vacuum pul1" is maintained throughout the metal shooting operation. These conditions are ditlicult to satisfy because in order for pressures as low as this to be established, the cross-sectional area of the evacuation passage in the die must be so large that molten metal forced into the die cavity during the shooting operation can flow into and thus obstruct the vacuum line. Since a die casting machine is a mass production device, it will be apparent that the delays entailed in clearing this line are intolerable.

Applicants copending application Serial No. 760,171, filed September 10, 1958, discloses a device (a parting line trap chamber which is connected with the die cavity by a parting line vent passage) which permits establishment of the required low pressure during the shooting operation without allowing molten metal to fiow into and clog the vacuum line. However, this device has one undesirable characteristic; it requires the use of a wide shallow parting line vent or evacuation passage. In multiple cavity dies having a number of core moving mechanisms, this is a very serious disadvantage because there is very little free space on the mating faces of the die members in which to locate the vent passages. Furthermore, this type of passage limits the pressure which can be established in the die cavity to about 9 or 10 inches Hg absolute.

The object of this invention is to provide an improvement in the device of the copending application men tioned above which permits the use of narrow deep vent passages and the establishment of pressures in the die cavity as low as 7 or 8 inches Hg absolute. According to this invention, the parting line vent passage connecting the die cavity with the trap chamber is equipped with a stop valve which is shiftable longitudinally of the passage between passage-closing and passage-opening positions. The movable element or head of the valve is biased toward its passage-opening position and carries a reaction surface which is subject to the impact of the molten metal flowing through the vent passage for shifting the valve to its passageclosing position. Since the valve is closed in advance of the movement of molten metal toward the trap chamber, vent passages of any desired States Patent Patented Feb. 14, 1961 size and shape can be used without risk of allowing an intolerable amount of metal to flow into the trap chamber. Furthermore, since the valve is closed by the molten metal in the vent passage, the vacuum pull is maintained on the die cavity up to the time this passage is filled.

The preferred stop valve incorporates several structural details of particular importance. First, the valve head is carried by a stem which is guided and supported by a bearing attached to the stationary die member and located on the side of the trap chamber opposite the vent passage. This arrangement ensures free movement of the valve because it prevents molten metal under pressure from being forced between the mating surfaces of the stern and the bearing. Second, the valve head is provided with a flat surface which slides along the face of the stationary die member, and with a U-shaped land which extends around the head from that surface and is arranged to cooperate with a peripheral valve edge formed in the movable die member. When the dies are opened after the shooting operation, the peripheral valve edge moves away from the valve land thereby exposing the metal which has solidified around this land and facilitating its removal. Finally, the connection between the stern-support bearing and the stationary die member permits the bearing to be moved away from the face of the stationary die mmeber when the dies are opened. This affords access to the space between the fiat surface on the valve head and the face of the stationary die and thus allows the operator to clean out any metal flash which may have been deposited in this region.

Although the invention is described herein in connection with a die cavity evacuation system, Le, a system which includes a pump for reducing the pressure in the die cavity, it will be apparent that it can be employed to advantage in those cases where the die cavity is merely vented to atmosphere. In the vented cavity die casting machine, the vent passage must be so designed that no molten metal is allowed to escape past the outer edges of the die members during the shooting operation. In the conventional machine, this requirement is satisfied by using wide, shallow vent passages. Because of this, rapid and complete expulsion of gases from the die cavity is not possible. The present invention is useful in this type of machine because it permits the use of much deeper vent passages and thus increases the rate of expulsion of the gases, and consequently the quantity expelled, during the shooting operation. As a result, castings produced by a vented cavity machine employing this invention tend to be less porous and have better surface finishes than those produced in the conventional manner.

The preferred embodiment of the invention will now be described in detail with reference to the accompanying drawing, in which:

Fig. 1 is a partial plan view of the stationary and movable die members of a bottom injection cold chamber die casting machine, together with a schematic diagram of the vacuum system with which they are used.

Fig. 2 is an enlarged elevation view of the face of the stationary die member shown in Fig. 1.

Fig. 3 is an enlarged sectional view taken on line 3-3 of Fig. 2 including the adjoining portions of the movable die member.

Fig. 4 is an enlarged sectional view taken on line 4-4 Fig. 7 is an end view of the valve head taken on line 7--7 of Fig. 5.

As shown in Fig. 1, the invention is embodied in the stationary and movable die members Ill and 12, respectively, of a bottom injection cold chamber die casting machine such as the one shown in US. Patent 2,103,438, issued December 28, 1937. The stationary die member 11 comprises a die block 13 and trap chamber housing section 14 which mate along parting line 15 with the corresponding components 13' and 14 of movable die member 12. The sections 14 and 14' are connected to die blocks 13 and 13 by bolts (not shown). T he mating face of each die member contains a gate 16 which leads from a pressure chamber 17 to the die cavity l8. As explained in copending application Serial No. 760,- 171, the lower end of the pressure chamber 17 is enlarged at 19 and the metal magazine 21 is extended upward into this enlargement. The mating faces of the die members are sealed by a resilient tube 22 of heat resistant silicone which is fitted in a groove that encircles the face of die member lit. A trap chamber 23 is formed on the parting line 15 in the trap chamber housing and extends into each of the sections 14, 14 thereof. The housing section 14 is provided with an outlet passage 24 which connects the trap chamber 23 with a threaded outlet port 25.

A parting line vent passage 26 is defined by the mating faces of the die members 11 and 12 for connecting die cavity 18 with trap chamber 23. The size and shape of the transverse cross-sectional area of this passage is selected solely with regard to the pressure which is to be established in the die cavity 18 since, as will be explained below, the invention provides means for preventing the flow of molten metal from the die cavity to the trap chamber through this passage. The vent passage comprises a first portion 27 of semi-circular shape in transverse cross-section which extends from the die cavity 18 to within a short distance of the edge of die blocks 12 and 12, a second portion 28 of rectangular shape in cross-section which extends between first portion 27 and the edge of the die blocks, and a third portion which extends between the second portion and trap chamber 23 and is formed by the face 29 of housing section 14 which lies on the parting line 15, and by three coaxial semi-circular bores 31, 32 and 33 formed in housing section lid. In a typical installation, the first portion 27 has a diameter of /2 inch, is about inches long, and extends to within inch of the edge of the die blocks, and the second portion 28 is 1 inch wide and 0.050 of an inch deep.

Communication, between die cavity 18 and trap chamber 23 through vent passage 26, is controlled by a stop valve 34. This valve includes a head 35 and a cylindrical stem 36; the head having a flat surface 37 which is in sliding engagement with face 29 and a semi-cylindrical valve land 38 which is coaxial with bores 31, 32, 33. The stop valve 3-5 is shiftable between a passageopening position (shown in Fig. 5) in which the left edge of land 38 is spaced from the peripheral valve edge 39 formed at the junction of bores 32 and 33 by about 0.075 of an inch, and a passage-closing position (shown in Fig. 6) in which the annular surface 41 on the valve head abuts the shoulder 42 defined by bores 31 and 32. When the die members are hot, the radial clearance between land 38 and bore 32 is about 0.002 of an inch. An equal clearance is provided between surface 37 and face 29.

The stem 36 of the stop valve 34 is supported and guided in a bearing block 43 which is held tightly between housing sections 14 and 14' when the die members are closed. The block 43 is connected with section 14 by four bolts 44 which are free to slide longitudinally in their bores 45 and are so dimensioned that they may move a short distance (indicated at 46 on the drawing) in a direction normal to the parting line when the die members are open. This limited movement permits access to the space between face 29 and the surface 37 for the purpose of removing any flash which may be deposited in this region during the shooting operation. A travel of A3 of an inch is deemed adequate. A spring 47, reacting between block 43 and a seat bolted to the end of stem 36, biases the valve 34 to the passage-open ing position shown in Figs. 2, 3 and 5.

In operation, threaded outlet port 25 is connected with a vacuum pump 48 by vacuum line 2$, shut-off valve 51, and receiver 52. The actuator 53, of the shut-off valve, is operated by the movable die member actuating mechanism, and when the die members are open, the shutoff valve is closed and the trap chamber 23 is isolated from the vacuum pump 48.

When the die members 11 and 12 are closed and the shut-off valve 51 is opened, the die cavity 18 is evacuated through vent passage 26, trap chamber 23, outlet passage 24, outlet port 25, and vacuum line 49. Since the vent passage 26 is deep, evacuation of the die cavity occurs almost instantaneously. Therefore, as soon as the die members are closed, the metal injection plunger is moved upward to force metal from the magazine 21 through pressure chamber 17 and the gate 16 into the die cavity 18. A portion of this metal is forced into and through vent passage 26, where it impinges upon the end face 54 of the valve head 35. The impact of the molten metal shifts stop valve 34 to the right (as viewed in Fig. 3) to its passage-closing position against the bias of spring 47. When this occurs, communication between vent passage 26 and trap chamber 23 will be interrupted and, as a result, molten metal will be prevented from entering trap chamber 23. Since the land 38 must move a short distance (0.075 of an inch in the typical case mentioned above) before it overtravels peripheral edge 39 and thus closes the vent passage, a small amount of metal flash will be forced into trap chamber 23. However, since the rate of flow of gases from this chamber to the vacuum pump 43 at this time is practically zero, this flash will not be sucked into vacuum line 9.

When the metal in die cavity 13 has solidified, the dies are opened and the cast part, together with the metal which solidifies in gate 16 and in vent passage 26 and the flash which deposits in trap chamber 23, is removed. Since peripheral valve edge 39 moves away from land 38 as the dies are opened, the metal which solidifies in bore 33 and around valve head 35 can be removed with no more effort than that normally required to eject the cast part from die cavity 18. In the normal case, no metal flash is deposited between face 29 and surface 37. This is probably attributable to the fact that the molten metal flowing along vent passage 26 loses so much heat that it is not fluid enough to pass through the small gap (0.002 of an inch in the example) between these members. However, in some cases, when using high injection pressures and very fluid casting alloys, a thin metal flash may be formed between face 29 and surface 37, but this flash does not interfere with the economical operation of the machine because of the fact that bolts :4 permit movement of stop valve 3 away from the stationary die member to thereby afford access to the space between these parts. It should be noted here that when the die members are closed, shoulder 4 2 limits the movement of valve 34 in the direction of its passage-closing position, but that when these members are opened, the shoulder moves away from valve head 35 and allows the h ad to move within trap chamber 23. This arrangement also affords access to the face 29 and the surface 37. Either access-affording arrangement may be used alone or both may be used together as in the preferred embodiment.

From Fig. 3 of the drawings, it will be observed that theportion 28 of vent passage Edslants downward toward the movable die member so that molten metal flowing along this passage does not enter the bore 33 along the face 29. This is a desirable arrangement when using very fiuid metals, but it is not essential.

It will also be observed that since the bearing lock 43 is located on the side of trap chamber 23 opposite the vent passage 26, the mating faces of the stem 36 and the bearing block are not subjected to molten metal under pressure. In the absence of the trap chamber 23, flash could be forced along the stem 36 to thereby prevent free sliding movement of the stem in the bearing block. The arrangement shown in the drawings is of extreme importance because it eliminates the delays which would be involved in freeing the valve stem between successive shooting operations.

As used herein, the terms parting line chamber and parting line passage mean chambers and passages that are intersected by the parting line in such manner that when the die members are open the interiors of the chambers and passages are exposed.

As stated previously, the drawings and description relate only to a preferred embodiment of the invention. Since many changes can be made in the structure of this embodiment without departing from the inventive concept, the following claims should provide the sole mea ure of the scope of the invention.

What is claimed is:

1. In a die casting machine including stationary and movable die members which join along a parting line and have cooperating faces that define the die cavity, a gate for delivering molten metal to the cavity, and a parting line trap chamber formed by the mating faces of the die members and having an outlet port, the improvement which comprises a parting line vent passage connecting the trap chamber with the die cavity; a stop valve located in the vent passage and having a seat and a movable element shiftable longitudinally of the passage between passage-closing and passage-opening positions; means biasing the movable element toward its passage-opening position; and a reaction surface carried by the movable element and subject to the impact of the molten metal flowing through the vent passage from the die cavity for shifting the element to its passage-closing position.

2. The improvement defined in claim 1 in which the movable valve element has a stem which extends across the trap chamber and a head which is located in the vent passage; and which includes a bearing connected with one of the die members and located on the side of the trap chamber opposite the vent passage for supporting and guiding the stem of the movable valve element.

3. The improvement defined in claim 2 in which the vent passage includes an enlarged portion at the trap chamber end, one wall of the enlarged portion being defined by a flat face on said one die member which is parallel with the parting line; in which the valve seat compirses a generally U-shaped peripheral valve edge formed in the other of said die members and extending around the vent passage from the flat face; and in which the valve head has a flat surface which is in sliding engagement with the fiat face and a land which is arranged to move into and out of sealing engagement with the peripheral valve edge.

4. The improvement defined in claim 3 in which the bearing comprises a block provided with a bore which tits and is in sliding engagement with the valve stem, said block being pressed tightly between the two die members when these members are closed; and which includes means connecting the block to said one die member but permitting limited movement of the block relatively to that member in a direction normal to the parting line when the die members are open.

5. The improvement defined in claim 4 in which the biasing means comprises a coil spring which is mounted within the block and reacts between it and the valve stem.

6. The improvement defined in claim 3 in which the peripheral valve edge is formed by the junction of two coaxial semi-circular bores in the other or": said die members; and the valve land has a semi-circular shape in transverse cross-section.

7. The improvement defined in claim 3 in which said that face of the enlarged portion of the vent passage is ofiset in the direction of said one die member relatively to the adjacent portion of the balance of the vent passage.

8. The improvement defined in claim 3 in which the flat face is located on the parting line; which includes a stop carried by the other of said die members for limiting the movement of the valve element in the direction of the passage-closing position when the die members are closed; and in which the parts are so dimensioned that the valve head may move to a position within the trap chamber when the die members are open.

References Cited in the file of this patent UNITED STATES PATENTS 1,627,784 Korsmo May 10, 1927 2,774,122 Hodler Dec. 18, 1956 2,866,240 Schroeder Dec. 30, 1958 2,867,869 Hodler Jan. 13, 1959 2,896,279 Nyselius July 28. 1959 2,914,822 Nyselius Dec. 1, 1959 

